THE EABTEQUAKE ADVANCE THEORY 181
"vigor than variations in precipitation could cause, and sufficient to explain the spasmodic advance and breaking of the glaciers that has been observed in the Yakutat Bay region. Since the unusual supply ceased as abruptly as it came, the advance quickly ran its course and the glaciers abruptly resumed their former condition.
A number of facts and considerations support this theory, as follows: (1) There was a series of unusually vigorous earthquakes in September, 1899. (2) Accompanying these shocks there was much avalanching. These two points are important in showing that the cause was actually present, though they do not prove that it was adequate. (8) Both the earthquakes of 1899 and the phenomena of spasmodically-advancing glaciers are centered in the Yakutat Bay region. (4) Of the advancing glaciers all but one are known to have begun their advance since 1899 and the evidence is all but conclusive that the other advance, that of the Galiano, occurred after 1899. (5) There has been a rough progression in the glacier advance from the smaller to the larger glaciers, beginning almost at once in the smallest, then affecting larger ones, then still larger, while the largest have not yet responded. (6) The duration of the advance was brief, indicating an intense cause of short duration. (7) The cessation of the advance was abrupt, indicating that the cause terminated abruptly. (8) The extent of the advance was great, involving the transfer of large masses of ice in thickening, spreading and pushing the glacier fronts forward, proving that the cause involved an extensive addition to the glacier supply. (9) The transformation of the glaciers is without recorded parallel, which indicates the necessity of seeking an unusual cause. (10) All other theories fail to satisfactorily account for the phenomena. (11) No facts observed are opposed to the theory of earthquake shaking. (12) The theory satisfactorily accounts for all the phenomena of the advancing glaciers.
It accounts for the location of the advancing glaciers in the Yakutat Bay region; for the beginning of the advance immediately after 1899 in the small glaciers; for its appearance in successive years in other, larger glaciers; for the failure of the largest glaciers to have responded as yet; for the failure of response of glaciers that did not receive numerous avalanches; for the pronounced breaking, advance and thickening of the glaciers; and for the sudden beginning and equally abrupt termination of the advance. Being the only theory that does not fail in some significant respects, having no vital points of objection, but on the contrary being supported by numerous important facts and considerations, and being competent to account for all the phenomena of the advancing glaciers, the theory of earthquake shaking occupies a strong position, falling little, if any, short of complete demonstration.
Nature of the Advance. It is made clear in the preceding chapters that several stagnant or nearly stagnant glaciers, with little if any crevassing, have undergone an abrupt change, becoming impassably crevassed and at the same time becoming thickened at then* lower ends and pushing forward at their fronts and margins; and that this period was of brief duration and terminated as abruptly as it began. Such an advance contrasts strikingly with normal motion of glaciers, as well as with the slow advance of a glacier under the influence of normal climatic variations, when through a period of years, and without notable change in surface conditions, the ice front gradually advances.
The reports of the International Committee on Glaciers show that between 1895 and 1907 the overwhelming majority of advancing glaciers in the Alps, Scandinavia, Russia, Canada, etc., moved forward from ten to sixty feet a year, there being one case of an